1. Field of the Invention
The present invention relates to an endoscope system that images an observation target in a subject, an endoscope system processor device, an operation method for an endoscope system, and an operation method for an endoscope system processor device.
2. Description of the Related Art
In the medical field, it is common to perform diagnosis using an endoscope system including a light source device, an endoscope, and a processor device. In particular, an endoscope system has become widespread that acquires an observation image, in which a specific tissue or structure such as a blood vessel or a ductal structure is emphasized, not only simply by imaging an observation target but also by finding the wavelength of illumination light to be emitted to the observation target or by performing signal processing, such as spectral estimation processing, on an image signal obtained by imaging the observation target.
In such an endoscope system, when the observation target is contaminated (due to adhesion of residue or colored mucus, for example) or when dye for coloring is used, a target specific tissue may not be appropriately emphasized, or dirt or the like may be emphasized, for example. Therefore, for example, in an endoscope system for highlighting the blood vessels disclosed in JP5191329B, dye contained in residue or the like is detected based on a spectral estimation image, and an image is generated by correcting the influence of the dye. In recent years, there has also been an endoscope system that acquires biological function information based on an image signal obtained by imaging the observation target. For example, diagnosis of a lesion using the oxygen saturation of blood hemoglobin has been performed. As a method of acquiring the oxygen saturation, a method is known in which first signal light and second signal light having different wavelength bands and different absorption coefficients for oxygenated hemoglobin and reduced hemoglobin are alternately emitted to blood vessels in the mucous membrane and reflected light beams of the first and second signal light beams are detected by a sensor located at the distal end of the endoscope (refer to JP5231511B).
The ratio of signal values (hereinafter, referred to as a signal ratio) of pixels of an image signal corresponding to the reflected light of the first signal light detected by the sensor and an image signal corresponding to the reflected light of the second signal light detected by the sensor is maintained as a fixed value if there is no change in the oxygen saturation in the blood vessel. However, if there is a change in the oxygen saturation, the signal ratio is also changed accordingly. Therefore, it is possible to calculate the oxygen saturation based on the signal ratio of the image signals.